1. Field of the Invention
The invention relates to an optical device with hybrid integrated laser chips and optical waveguide chip. In particular, the invention relates to an optical device using flip-chip method to hybrid integrate one or more laser chips with one optical waveguide chip with the help of optical bench chips with “U” shaped alignment optical waveguides having various waveguide distances.
2. Description of the Related Art
The internet based data applications such as social networks, cloud service, big data analysis and high performance computing have been the driving force to boost the bandwidth requirement to an unprecedented level. With the increase of bandwidth and transmission reach, optical interconnects have become the number one choice in data communication systems. Unlike traditional telecommunication systems, lower cost, more compact and more power efficient optical transceivers or engines are highly demanded in data communications. Integrating multiple optical components or chips such as lasers, modulators, photodetectors etc. to form a hybrid integrated optical device is a promising way to reduce assembling cost and footprint.
Laser chip hybridization usually requires turning on the laser chip so that the device chip can be actively aligned to the laser chip. To build the electric connection, the laser chip has to be fixed in a substrate first and connected to the power supply through wire bonding process. However, it becomes extremely challenging when dealing with multiple laser chips aligning with one optical device chip. In this scenario, the optical device chip needs to be fixed on a substrate first, and then the laser chips have to be actively aligned with the optical device chip one by one. It is very difficult to construct the electrical connections when the laser chips are floating for active alignment process.
Passively placing and bonding laser chips with optical waveguide device chips is highly desirable in such hybrid integrated optical devices for its potentials of low cost assembling for massive volume production. Unlike the mature integrated circuit (IC) fully automated packaging processes, optical integration requires very precise alignment in the range of micrometers or less to form an optical transmission path. It becomes very crucial when dealing with the integration of a laser chip with an optical waveguide chip, where two small waveguides need to be aligned with micrometer or sub-micrometer accuracy.
The alignment accuracy in the direction perpendicular to the chip surface (out-plane) can be controlled well by using a flip-chip bonding process, where one chip is placed upside down onto another chip. However, it is very challenging to achieve higher alignment accuracy in the directions parallel to the surface (in plane). A modern top-of-the-line flip-chip bonder can achieve a +/−0.5 micrometer alignment accuracy, however, in practice, the bonding involving processes such as thin metal solder melting, adhesive curing and etc. inevitably contribute to final alignment error due to physical movement of the chip under temperature, stress and/or phase changes. The final alignment error (3σ confidence interval) is usually +/−2 micrometers or worse from the statistics data. The alignment in in-plane waveguide propagation direction is relatively tolerant and satisfied with this alignment error while the in-plane direction perpendicular to waveguide propagation requires very accurate alignment, for example a sub-micrometer accuracy for small optical waveguides such as those in lasers. To increase the alignment tolerance in this direction, many approaches have been attempted. However, none of them is being adopted in mass production due to their limitations.